diff --git a/README.md b/README.md
index 0754f280..d223d174 100644
--- a/README.md
+++ b/README.md
@@ -26,8 +26,10 @@ If you want to support us in translating Kimai, please [read this documentation]
 ### Requirements
 
 - PHP 7.1.3 or higher
-- One PHP extension of [PDO-SQLite](https://php.net/manual/en/ref.pdo-sqlite.php) or [PDO-MySQL](https://php.net/manual/en/ref.pdo-mysql.php) enabled (it might work with PostgreSQL and Oracle as well, but that wasn't tested and is not officially supported)
-- The PHP extension [intl](https://php.net/manual/en/book.intl.php)
+- The PHP extensions:
+  - [PDO](https://php.net/manual/en/book.pdo.php) (with either [pdo_sqlite](https://php.net/manual/en/ref.pdo-sqlite.php) or [pdo_mysql](https://php.net/manual/en/ref.pdo-mysql.php) enabled)
+  - [intl](https://php.net/manual/en/book.intl.php)
+  - [zip](https://php.net/manual/en/book.zip.php)
 - The [usual Symfony application requirements](http://symfony.com/doc/current/reference/requirements.html)
 - If you use MariaDB, make sure its at least v10.2.7 (see [FAQ](var/docs/faq.md))
 - Kimai needs to be installed in the root directory of a domain or you need to [recompile the frontend assets](var/docs/developers.md)
diff --git a/composer.json b/composer.json
index ec463681..5f23d2c2 100644
--- a/composer.json
+++ b/composer.json
@@ -7,7 +7,7 @@
         "php": "^7.1.3",
         "ext-intl": "*",
         "ext-pdo": "*",
-        "ext-pdo_sqlite": "*",
+        "ext-zip": "*",
         "beberlei/DoctrineExtensions": "^1.0",
         "erusev/parsedown": "^1.6",
         "friendsofsymfony/rest-bundle": "^2.3",
diff --git a/var/docs/developers.md b/var/docs/developers.md
index 3d769c37..fef2fb9d 100644
--- a/var/docs/developers.md
+++ b/var/docs/developers.md
@@ -6,19 +6,17 @@ This page is dedicated to all developers who want to contribute to Kimai. You ar
 
 All you need is:
 - PHP >= 7.1.3
-- PHP extension: `PDO-SQLite` enabled
+- PHP extensions: `PDO-SQLite`, `intl` and `zip`
 
 Optional requirement:
 - a MySQL/MariaDB instance
 - PHP extension: `PDO-MySQL` enabled
 
-You could even test PostgreSQL and tell us how it works!
-
 Read how to [install Kimai v2 in your dev environment](installation.md). 
 
 ## Frontend dependencies 
 
-If you want to make changes to CSS / Javascripts, you need:
+If you want to make changes to CSS / Javascript, you need:
 
 - [NodeJS](https://www.npmjs.com/)
 - [Yarn Package Manager](https://yarnpkg.com/en/)